Method and apparatus for measuring the thickness of an object



May 10,1966 w. ROBERTS 3,250,119

METITIOD AND APPARATUS FOR MEASURING THE THICKNESS OF AN OBJECT Filed June 28 1962 2 Sheets-Sheet 2 I" I 64$ 64 1 l L2 I t u e f. a

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INVENTOR. WILL/1M L. ROBERTS AHarney United States Patent Of fice 3,250,119 Patented May '10, 1966 3,250,119 METHOD AND APPARATUS FOR MEASURING THE THICKNESS OF AN OBJECT William L. Roberts, Murrysville, Pa assignor to United States Steel Corporation, a corporation of Delaware Filed June 28, 1962, Ser. No. 206,029 7 Claims. (Cl. 7367.2)

This invention relates to a method and apparatus for measuring the thickness of an object and more pa.- ticularly to measuring the thickness of a slab of steel being fed to a rolling mill. When a slab of steel is removed from the heating furnace it is first conveyed to a scale breaker before being further processed in a hot rolling milL If the roll gap of the scale breaker is not set at approximately the thickness of the slab, breakage of the rolls and other parts of the scale ,brealter often c curs. This difficulty may be mitigated if the thickness of each slab is measured as the slab emerges from the heating furnace and if the roll gap in the scale breaker is set accordingly. Various existing thickness measuring devices are unsatisfactory for this purpose. Devices utilizing optical techniques are inaccurate due to the steam and dust which surrounds the slab at this point. Contacting devices have the disadvantage that only the thickness at a single'point is measured. X-ray and radioisotopic gaging are not satisfactory because the thickness of the steel to be measured is approximately 3 to 20 inches which is beyond the useful operating range of a radiation-type gage.

It is herefore an object of my invention to provide a method of measuring the thickness of an object without contacting it.

Another object is to provide apaprzrns for measuring the thickness of an object without contacting it.

A further object is to provide such apparatus that will measure the average thickness of an object in such manner-that the effects from small surface variations will not cause inaccuracies.

These and other objects will be more apparent after referring to the following specification and attached drawings, in which:

FIGURES 1A and 13, when united on the lines-A-A and B-B form a schematic view of the apparatus of my in ention.

Referring more particularly to the drawings, reference numeral 2 indicates a roller conveyor v-hich transports a slab of steel S from a reheating furnace to a scale breaker or other apparatus, not shown. The conveyor 2 includes a plurality of rolls 4 which are supported in conventional bearings, not shown, on a horizontal member 6 and are driven by conventional means, not shown. The member 6 is supported by vertical members 8 and 10 which have conventional load'cells 12 acd 14, respectively, therein. The members 8 and 10 are preferably made of steel so that they have elasticity and are sup ported at floor level 15. The members bearing the refcrence numerals 6 through 14, inclusire, are duplicated with respect to the other end of rolls 4, but because they are identical, they are not shown. The load cells 12 and 14 are connected in series to a conventional bridge amplifier 16 which produces an output voltage proportional to the weight of the slab S. An example of a suitable bridge amplifier 16 is .\lodel No. BAM-l manufactured 175 which assumes an angular position corresponding to the weight on Lhe loaded table. The voltmeter 17 may be a Model No. 4510 RDP of Electra instruments,

Inc, San Diego. California.

v I A pneumatic cylinder 18 is rigidly supported by a memher 20 and has a piston 22 which carries piston rod 24. The free end of the rod 24 is adapted to contact the vertical member 8 when air under pressure is supplied to cylinder 18 through solenoid valve 26 having an operating solenoid 26S.- Air is exhausted'from .the cylinder 18 through a solenoid valve 28 having an operating solenoid 288. Power from a power source 29 is supplied to the solenoid 268 through a nonnally closed contact 30C of a relay 30 which also has a normally open contact 30C1. Power source 29 is connected to solenoid 288 through contact 30C1. A plurahry of phototubes 32 are mounted above the rolls 4 and rap-0nd to the presence of the hot slab S. Phototubes 32 are connected to a conventional amplifier 34, the output of which is connected to the coil of relay 30. Y

One end of a rod 36 is rigidly attached to the member 10 and the other end has a permanent magnet 38 attached thereto. A coil 40 is supported by a member 42 extending to the floor 15 and is so arranged that its turns encircle the magnet 38 and are free to move with respect thereto. Each end of coil 40 is connected to the input of a counter-gate unit 44 which may be a conventional device such as Model So. 7160 described at page 1-2 of Catalogue 705, 1957, of the Beckman-Berkeley Division of Beckman Instruments, Inc. To the binary outputs of the counter-gate unit 44 is connected a digital to ana-' log converter 45 which comprises a plurality of relay coils 46, each having a normally closed contact 46C. A resistor 48 is connected areas each contact 46C in parallel with a series combination of a resistor 50 and a battery 52. Each paraliel combination is then connected in series with the others so as to produce at output terminals 54 and 56 a voltage pro;ortional to the count registered by the counter-gate 4-1. The counter-gate 44 amplifies the. sinusoidal vibrauoasignal developed by magnet 38 and coil 40 and one half cycle of the amplified signal is used as a gating imrl se in a circuit of the countergate 44 so that the circit which receives impulses at a high repetition rate is opened for the duration of the gating pulse. Thus thenumber of high frequency impulses passing through fie circuit-is proportional to the period of the vibration. These high frequency impulses and 62? ganged together and mechanically connected to shaft 585. Switch 60 bzludes resistors 60A, 60B, 60C, 60D, 60E, 60F. 60G ari 60H which are preferably of equal value. -The terminals of switch 60 are connected to a DC. power source L1. L2 having a voltage V1. The switch 62 includes "to-s 62A, 62B, 62C, 62D, 62E, 62F, 620 and 62H pre :ly of equal value. Pole GOP is connected to one terz: ll. of switch 62 and the other terminal of switch 62 is annealed to line L2. A potentr ometer 64 having slider 545 is connected across the terminals of switch 60. A rstary switch 66 has its pole 66? connected for rotation vii: shaft 175. Pole 66? is electrically connected to pole 62?. Switch 66 includes resistors 66A, 66B, 66C. 65D, 66E. 66F, 666 and 661-1 preferably of equal value. .The terminal of switch 66 adjacent resistor 66H is -connccted to slider arm 645 through a resistor 68:- A conventional digizal voltmeter 70 is connected across resistor 68. Th e digital voltmeter 70 may be of the same age as voltmeter 17 and rs pro- 7 vided with a shaft 705 mechanically connected to pole 72? of a rotary switch 72 which has resistors 72A, 72B, 72C, 72D, 72E, 72F, 726 and 72H, all preferably of equal value.- The terminals of switch 72 are connected to a DC. power source L3, L4 having a voltage V2. A potentiometer 74 having a slide wire 745 is also connected across the terminals of switch 72. The pole 72F and slider 745 are connected to a voltmeter 76.

The basis of the measurement of thickness is as follows: Assuming that the moment of inertia of the table 6 without the workpiece S thereon about the base of its legs 8 and 10 is JE and the restoring torque per unit of angular displacement of legs 8. and 10 caused by their elasticity is T then the period of oscillation PE of the empty table is given by the-W PE'J' 7 Equation 1 When the workpiece S is supported on the table the moment of inertia of the assembly is increased by a quantity M(L+d/2)"' where M is the mass of the workpiece, L is the height from the floor to the bottom surface of the workpiece and dis the thickness of the workpiece. Thus, when the workpiece is on the table the period of oscillation PI. is given by the equatign:

JE+M(L+d.2)* PL 2T T Equation 2 B combinin E uationsl and2the followin e uat'on y g q g q 1 30 Iclaim:

is obtained:

In operation, the positions of the poles 60? and 62P are proportional to the period of oscillation PL of the table and slab since the poles are connected to the shaft 588. Thus, the potential difference between the pole 6UP and the end of resistor 60H is proportional to PL when the resistors 60A to 60H are of equal value. The potential difference between the pole 62? and the end of resistor 62H is proportional to PB. The slider 645 of the potentiometer 64 is adjusted so that the potential between it and point 78 is proportional-to PE. Hence, the potential difference between poles 62? and slider 643 is made proportional to PU minus PE. This signal is applied to the circuit consisting of switch 66 and resistor 68. Since the angular position of the pole 66? is proportional to the weight M of the slab, the resistance between pole 66F and point 80 is made proportional to the weight M of the workpiece and since the resistor 68 has a relatively small value the current in the circuit is proportional to pearing between the pole 72? and point 82 being proportional to PL"--PE v M By suitable choices of circuit parameters the voltage between pole 72F and point 82 is made equivalent to HE A..

J1 PL since 1E and PL are constants for g en equipment. The slider'74S is set so that the otential hereen point 82 and slider 745 is equivalent to L. Therefore, a signal 7 exists between pole 721 and slidr 74S hich is proportional to cause sufficient vibration so that it would be measured by means 0 tthe vibration pick-up 36, 38 and 40 the vibration means 18, 22 and 24 is preferably used. Thus, when a hot slab S is received on the table 6 the phototubes 32 will be activated and the signal therefrom willbe amplified by amplifier 34 and will energize the coil of relay 30, thus closing contact 30C! and opening contact 30C. Closing of contact 300 energizes solenoid 288, thus exhausting air from cylinder 18. Opening of contact 30C deenergizes solenoid 265 so as to close valve 26. When the table 6 is not supporting a hot workpiece the phototubes 32 will be deenergized and the contacts 30C closed and contacts 30C1 open so that the table is strained by the pressure ofthe piston rod 24. Thus, release of.this pressure will cause vibration of the table 6.

While one embodiment of my in ention has been shown and described, it will be apparent that other adaptations and modifications may be made without departing from the scope of the following claims.

1. Apparatus for measaring a lineal dimension of an object comprising an elg gated support for said object with the configuration of the object so supported being such that its center of mass is in a plane parallel to said support a distance therefrom of known proportion to the said lineal dimension, elastic meansattnghedlsaid elongated support adjacent t e ends thereof and extending therefrom generally normal thereto, means for weighing said object, means for oscillating said supported object in a plane generally normal to the dimension to be measured, means for measuring the period pf g sc llgt gr oLsa d go eer and means responsive to saidwmgmngagd meas uring means or computing ihe gafidjineal dimppsigp of said object.

2. Apparatus for measuring the thickness of an object comprisingan elongated generally horizontal support for said object with the configuration of the object so supported being such that its center of mass is in a plane parallel to said support a distance therefrom of known proportion to the said lineal dimension, a generally vertical elastic support attached to said elongated support adjacent the ends thereof and extending downwardly therefrom, means for weighing said object, means for oscillating said object and said supports in a generally horizontal plane,'means for measuring the naturai frequency of oscillation of said object and said supports, and means responsive to said weighing and measuring means for computing the average thickness of said object.

3. Apparatus according to claim 2 in which said computing means comprises means for converting the output of said measuring means into a voltage, means responsive to said converting means for squaring said voltage, means for producing a voltage proportional to the square of the period of the natural frequency of oscillation of said supporting means, means responsive to said last two means for producing a voltage proportional to the difference between said last two means, means responsive to said weight determining means for attenuating the signal produced by said last named means by an amount proportional to the out ut of said weighing means, means responsive to said attenuating means for gen rating a signal 5 means for producing a voltage proportional to the difference between said last two means, and means responsive to the last said means for visually displaying the magnitude of the signal produced by said means.

4'. Apparatus for measuring the thickness of an object 'according to claim 2 in which said 'aeigh'ing means includes load cells connected to said vertical elastic support.

5. The method of measuring a lineal dimension of an object which comprises weighing said obiect on a support with the configuration of the object being such that its center of mass is in a plane parallel to said support a distance therefrom of known proportion to the lineal dimension, oscillating said object in a plane normal to the dimension to be measured, measuring the period of oscillation of said object, and correlating the weight and oscillation measurements to obtain the said lineal dimension of the object.

i 6, The method of measuring the thickness of an object which comprises placing said object on a support a known distance above a supporting base with the configuration of the object so placed being such that its center of mass is in a plane parallel to said support a distance therefrom equal. to one half of the said thickness, weighing said object on said support, oscfllating said object and support at their natural frequency in a plane normal to the said thickness, measuring the periods of oscillation of said object and support, and determining t'r.-e thickness of said object according to the equation:

wherein d=thickness oi the object JE=moment of inertia of-the empty support about its supporting has:

PE=periCd of oscillation of the empty support PL=period of oscillation of the support and object M =wcight of the object L=distrmce between the supporting base and bottom of the obecL t 7. Apparatus for measuring the thickness of an obiect comprising a generally horizontal support for said object with the configuration of the object so supported being such that its center of mass is in a plane parallel to said support a distance therefrom of known proportion to said lineal dimension. 2. generally vertical elastic support attached to said eZcngated support adjacent the ends thereof and extending downwardly therefrom, means for transporting said object to said horizontal support, means for measuring the pencd of the natural frequency of oscillation of said objsa and said supports, means for weighin; said objecz, and means responsive to said weighing "2,694,310 ll.l9 54 Pounds 73-67 3,059,468 10-1962. .Rowe 73-672 3,080,750 311963 \Viley a 7367.2X

RICHARD C. QL'EISSER, Primary Examiner.

JOHN A, BEAL'CHAMP, Examiner.

CHARLES A. RUEHL, Assistant Examiner. 

1. APPARATUS FOR MEASURING A LINEAL DIMENSION OF AN OBJECT COMPRISING AN ELONGATED SUPPORT FOR SAID OBJECT WITH THE CONFIGURATION OF THE OBJECT SO SUPPORTED BEING SUCH THAT ITS CENTER OF MASS IS IN A PLANE PARALLEL TO SAID SUPPORT A DISTANCE THEREFROM OF KNOWN PROPORTION TO THE SAID LINEAL DISMENSION, ELASTIC MEANS ATTACHED TO SAID ELONGATED SUPPORT ADJACENT THE ENDS THEREOF AND EXTENDING THEREFROM GENERALLY NORMAL THERETO, MEANS FOR WEIGHING SAID OBJECT, MEANS FOR OSCILLATING SAID SUPPORTED OBJECT IN A PLANE GENERALLY NORMAL TO THE DIMENSION TO BE MEASURED, MEANS FOR MEASURING THE PERIOD OF OSCILLATION OF SAID OBJECT, MEANS RESPONSIVE TO SAID WEIGHTING AND MEASURING MEANS FOR COMPUTING THE SAID LINEAL DIMENSION OF SAID OBJECT. 